(1) Field of the Invention
This invention relates to a method and apparatus for separating a protective tape together with a separating tape through joining the separating tape to the protective tape joined to a surface of a semiconductor wafer (hereinafter, simply referred to as “wafer”) having a pattern formed thereon, and then separating the separation tape.
(2) Description of the Related Art
After completion of a pattern forming process, a protective tape is joined to a surface of a wafer, and a back grinding process is uniformly performed to the entire rear face of the wafer. Thereafter, the protective tape is separated from the surface of the wafer, and then the wafer is subjected to a dicing process in which the wafer is divided into chips.
According to a method of separating the protective tape from the surface of the wafer, the wafer is suction-held on a table while the surface, to which the protective tape is joined, of the wafer is directed upward. Then, a separating adhesive tape is joined to the protective tape with a joining roller. Thereafter, the adhesive tape is folded back and separated with an edge member. Accordingly, the protective tape joined to the adhesive tape is separated together from the surface of the wafer. See, Japanese Patent Publication No. 2002-124494.
Recently, the wafer needs to be thinner in response to rapid advance in application. The wafer needs to be thinned to have a thickness of 100 μm to 50 μm, sometimes to around 25 μm. Such a thin wafer having the protective tape joined to the surface thereof is brittle and readily to bend, which leads to difficulty in handling. Accordingly, an annular projection is formed remaining at an outer periphery of the rear face of the wafer as to surround a region where a back grinding is to be performed. Thus, the wafer is reinforced.
When the protective tape is separated from the surface of the wafer surface after a back grinding process, only the annular projection on the rear face of the wafer is brought into contact with the holding table to be suction-held, and fluid is supplied between the holding table and the rear face of the wafer for realizing enhanced internal pressure. The separation tape is joined to the protective tape under this state while traveling and being pressed with the separating member, and is folded back for separation, whereby the protective tape joined to the adhesive tape is separated from the surface of the wafer together with the adhesive tape. See Japanese Patent Publication No. 2008-34709.
The conventional apparatus, however, has the following problem. That is, when the separation tape is joined to the protective tape, clogging may occur on a suction-holding line of the holding table at a position where joining of the separation tape starts, or suction ability may be degraded or eliminated due to failure in a pump. When the separation tape having degraded suction ability is separated, the tension in the separation tape becomes higher than suction to a wafer. The tension may lead to floating of the wafer from the holding table while the wafer is warped. As a result, poor separation and fracture in the wafer may occur. This problem may arise in the apparatus disclosed in both prior arts.
Moreover, in the apparatus disclosed in Japanese Patent Publication No, 2008-34709, the tension in the separation tape is concentrated on a joint portion of the annular projection on the rear face of the wafer and the thinned flat surface inside thereof. As a result, another new problem may arise that a crack is generated in the wafer from the joint portion.